text: Usually, only a small sample is dissolved in an appropriate solvent. For H NMR experiments, this will usually be a deuterated solvent such as CDCl. Sufficient solvent should be used in order to fill the tube by 4–5 cm (depending on the spectrometer). Protein NMR is usually performed in a 90% HO (or buffer)/10% DO mixture.
  The sample may be sonicated or agitated to aid dissolution, and solids are removed via filtering through a plug of celite layered on a cotton wool plug in a Pasteur pipette, directly into the NMR tube.
  The NMR tube is then usually sealed with a polyethylene cap, but can be flame sealed or sealed with a Teflon Schlenk tap or even a very small rubber septum. Parafilm may be wrapped around the cap to reduce solvent evaporation.